Making the Invisible Visible

Insights into the mechanisms of chemical transformations yields knowledge about tuning and controlling material properties. The evolution of transient species and phases formed during reactions poses challenges for ex situ observation, complicating optimization for many material classes. In this context, in situ probes play a pivotal role and provide information about crystallization pathways, crystal orientation, formation dynamics, and metastable phases, among other aspects. I will discuss the application of multimodal in situ probes to characterize the formation of different materials including 3D and 2D organic-inorganic halide and oxide perovskites. Halide perovskites have emerged as a promising material class for high-efficiency photovoltaics at affordable cost. The field moved towards more complex compositions and material combinations enabling improved device performance and stability. Most of the improvements however, were achieved through empirical optimization of processing conditions. The fast and complex chemical reactions lead to significant variations in material properties. In this regard, precise control over device performance requires a better understanding and active control over synthetic parameters, thus in situ monitoring of evolving properties can help identify synthesis and structure-property relationships. By using synchrotron-based diffraction measurements coupled with photoluminescence characterization during thin film fabrication, the early stages of nucleation and short-lived intermediates can be unveiled. Collaborative work on the effect of antisolvent dripping and additive-assisted crystallization approaches will be discussed and linked to photovoltaic performance. Mechanistic insights from experimental findings are supported by theoretical calculations provided by our collaborators. The synchrotron work is a result of fruitful collaborations with colleagues at the Advanced Light Source. I will conclude by sharing our joint work with Molecular Foundry scientists and collaborators by introducing AutoBot – a robotic platform for thin film fabrication and characterization. Its application underscores the benefit of systematic parameter screening in identifying relevant thin film fabrication variables to enhance reproducibility.